Shell Scripting – Shopt Command

Last Updated : 17 Oct, 2022

Unlike many shell commands, shopt is a bash-only shell command. It is a built-in BASH shell command that controls certain options for the shell session. One can consider this as a boolean ON/OFF switch for certain shell options. The “shopt” command provides control over many settings that are used to tweak the operations in a Bash shell. The number of options are available for the “shopt” command varies from version to version; older versions will have fewer commands compared to newer versions.

Syntax:

shopt [arg] [optname...]

The different values of arg and optname will be discussed below sections.

Values of the argument arg

arg	description
-o	Restricts the optname values to those of the built-in set command
-p	Prints the current values of all shell options.
-q	This is the quiet mode; provides no output but, returns an error status. For the single optname provided, this return status TRUE(0) if the option is set, else it returns FALSE(non-zero). For multiple optname(s) provided, this return error status TRUE(0) if all the given options are set, else return FALSE(non-zero).
-s	Sets the given optnames. If none is given then, displays all the set options.
-u	Simply unsets the options given.

Values of the optname options

The following table displays the options given to the shopt command’s optnames.

optname	description
autocd	If set, a command name that is the name of a directory is executed as if it were the argument to the cd command. This option is only used by interactive shells.
cdable_vars	If set, an argument to the cd built-in command that is not a directory is assumed to be the name of a variable whose value is the directory to change to.
cdspell	If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected filename is printed, and the command proceeds. Interactive shells only use this option.
checkhash	If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed command no longer exists, a normal path search is performed.
checkjobs	If set, bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs are running, this causes the exit to be deferred until a second exit is attempted without an intervening command The shell always postpones exiting if any jobs are stopped.
checkwinsize	If set, bash checks the window size after each external (non-builtin) command and, if necessary, updates the values of LINES and COLUMNS. This option is enabled by default.
cmdhist	If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy re-editing of multiline commands. This option is enabled by default but only has an effect if command history is enabled.
compat31	These control aspects of the shell’s compatibility mode.
compat40
compat41
direxpand	If set, bash replaces directory names with the results of word expansion when performing filename completion. This changes the contents of readline editing buffer. If not set, bash tries to preserve the user typed input.
dirspell	If set, bash attempts spelling correction on directory names during word completion if the directory name initially supplied does not exist.
dotglob	If set, bash includes filenames beginning with a ‘.’ in the results of pathname expansion. The filenames ”.” and ”..” must be matched explicitly, even if dotglob is set.
execfail	If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the built-in exec command.
expand_aliases	If set, aliases are expanded. This option is set by default for interactive shells.
extglob	If set, the extended pattern matching features are enabled.
extquote	If set, $’string’ and $”string” quoting is performed within ${parameter} expansions enclosed in double quotes. This is enabled by default.
failglob	If set, patterns that fail to match filenames during pathname expansion result in an expansion error.
force_fignore	If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word completion even if the ignored words are the only possible completions. This is set by default.
globstar	If set, the pattern ** used in a pathname expansion context will match all files and zero or more directories and sub-directories. If the pattern is followed by a /, only directories and sub-directories match.
gnu_errfmt	If set, shell error messages are written in the standard GNU error message format.
histappend	If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exists, rather than overwriting the file.
histreedit	If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution.
histverify	If set and readline are being used, the results of history substitution are not immediately passed to the shell parser. Instead, the resulting line is loaded into the readline editing buffer, allowing further modification.
hostcomplete	If set, and readline is being used, bash will attempt to perform hostname completion when a word containing a @ is being completed. This is set by default.
huponexit	If set, command substitution inherits the value of the exit option, instead of unsetting it in the subshell environment. This option is enabled when POSIX mode is enabled.
interactive_comments	If set, allows a word beginning with # to cause that word and all remaining characters on that line to be ignored(commented) in an interactive shell. This is set by default.
lastpipe	If set, and the job is not active, the shell runs the last command of a pipeline not executed in the background in the current shell environment.
lithist	If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines rather than using semicolon separators where possible.
mailwarn	If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the message ”The mail in mailfile has been read” is displayed.
no_empty_cmd_completion	If set, and readline is being used, bash will not attempt to search the PATH for possible completions when completion is attempted on an empty line.
nocaseglob	If set, bash matched filenames in a case-insensitive fashion when performing pathname expansion.
nocasematch	If set, bash matches patterns in a case-insensitive fashion when performing matching while executing case or [[ conditional commands, when performing pattern substitution word expansion, or when filtering possible completions as part of programmable completion.
nullglob	If set, bash allows patterns which match no files to expand to a null string, rather than themselves.
progcomp	If set, the programmable completion facilities are enabled. This option is enabled by default.
promptvars	If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal after being expanded. This is set by default.
shift_verbose	If set, the shift built-in prints an error message when the shift count exceeds the number of positional parameters.
sourcepath	If set, the source (.) built-in uses the value of PATH to find the directory containing the file supplied as an argument. This is set by default.
xpg_echo	If set, the echo built-in expands backslash-escape sequences by default.

Now, providing a description of all these options is a clumsy task therefore, in the next section it is shown how can one find the proper description of these options in the 6000+ lines long bash manual.

Accessing bash manual

The bash manual is highly descriptive and easy to access if one knows how. To open the bash manual, type the following command:

man bash

Now, it is a highly technical manual and scrolling to search for one keyword is hectic luckily, a simpler way exists. Once the manual is open, type / followed by the keyword you need a description about then, press enter.